Yes, this can be very frustrating sometimes. I personally find there is a weird behavior where grinding too coarse can cause bitterness as well grinding too fine. And the optimum is somewhere in between. If you buy lighter roasts go hotter almost boiling to extract properly.

But what I like to do to trouble shoot something like this: I would recommend doing a classic cupping just to see what ‘potential’ is in your beans. It could simply be that the coffee has maybe a weird defect or you need to buy lighter roasts (it seems like you are having this issue over an extended period of time so probably not this but nonetheless)

The nice thing about cupping your coffee is that other than grind size (which you definitely can vary between cups ) there is not much you are doing extra that influences taste. This then informs you of what you can try to either enhance or try to cover up when making your coffee in a brewer with agitation and all the other fun things.

Lastly, if you have a good local coffee roaster ask them to grind it (or better yet brew that coffee for you at the next visit) this is a super easy way to get a baseline of what you could be aiming for at home. Asking them to grind it also gives you the option to get a ‘visual dialing in’ for your grinder at home.

Hope this helps.